What is P&ID ? How to read a P&ID?


What is P&ID?

It stands for Piping and Instrumentation diagram.

It gives the over all idea about the process.

Why to use P&ID?

To describe over all plant and instrumentation.

It shows the flows in a plant and the corresponding sensors or other equipment.

It gives name to each sensors and other equipment along with their parameter.

P&ID :

The P&ID mixes pneumatic / hydraulic elements,electrical elements and instrumentation on the same diagram.

It uses a set of symbols defined in the ISA S5.1 standard

Examples of hydraulic / pneumatic symbols

P&ID Should be included with

All process equipment (With its tag number)

All pipes (With line number)

All valves with identification no along with their type and size should be shown.

Pumps with tag number

All control loops and instruments with identification.

Common Connection Lines

P&ID Connection

How to read P&ID ?

Discrete instruments are indicated by circular elements

Shared control/display elements are circles surrounded by a square.

Computer functions are indicated by a hexagon

Programmable logic function are shown as a triangle inside a square.




1st letter

P - Pressure
L - Level
T - Temperature
F - Flow

2nd Letter
I - Indicator
R - Recorder
C - Controller
T - Transmitter


instrument location

No Line - Instrument is mounted in the field near process (Close to the operator)

Solid line - The instrument is mounted in the control room (accessible to the operator)

Dotted line - The instrument is mounted out of sight (not accessible to the operator)